text:
What is the legally accepted tolerance for altimeter errors under EASA for a VFR flight?
I have a discussion going on with a flying club member.
He states that altimeters may have an error margin of up to +/- 200ft. Example: ATC instructs you to fly 1500 feet, you would still stick to their instructions when flying 1300/1700ft as they could not find out what the actual altitude is indicated on the altimeter, but only get Transponder FL reading + correct from pressure deviation.
We both agree, though, that sticking to the altitude indicated on the altimeter is the best thing to do.
It's more of a hypothetical discussion: Assume the altimeter displays 200ft more than the actual altitude (while correct QNH/Altimeter setting is dialed in), it could mean I'm intersecting the vertical border of a restricted area, believing I'm 200ft above it.
We tried to look up in EASA documents, but weren't able to find any guidance. The farthest we come are manufacturer tolerances upon delivering the devices and that systems need to be calibrated.
Can somebody shed some light on this and reference the legally relevant documents?
Assumptions: VFR flight in Europe/under EASA regulations, daytime, SEP.

Related: https://aviation.stackexchange.com/questions/71702/what-is-the-maximum-allowed-difference-between-two-altimeters-for-flying-in-rvsm

He may be conflating checkride or ATC standards for how closely a pilot is expected to maintain altitude, with tolerances for how accurate the instrument is required to be.

The relevant information is contained within ICAO Document 8168  Volume 1 Part 3

A serviceable altimeter indicates the elevation of the point selected, plus the height of the altimeter above this point,
within a tolerance of:
a) ±20 m or 60 ft for altimeters with a test range of 0 to 9 000 m (0 to 30 000 ft); and
b) ±25 m or 80 ft for altimeters with a test range of 0 to 15 000 m (0 to 50 000 ft).

I believe it is also worth pointing out that those values are only applicable for aerodrome elevations up to 3500 feet as stated in Notes 2 and 3 just below the cited paragraph in ICAO Doc. 8168.
For higher airport elevations (up to 15,000 feet), up to +- 225 feet from the correct reading is acceptable (Table III-1-3-2).

Depending how the altimeter was certified, it shouldn't be that far off unless you are up at 35,000 ft. Altimeters that are certified under ETSO-C10B/C must meet AS8009B/C. If the altimeter is also certified under ETSO-C106A, then some of the tolerances at the higher altitudes are tighter as well.

Altitude
Equivalent pressure (inches of mercury)
Tolerance ±(feet)

−1,000
31.018
20

0
29.921
20

500
29.385
20

1,000
28.856
20

1,500
28.335
25

2,000
27.821
30

3,000
26.817
30

4,000
25.842
35

6,000
23.978
40

8,000
22.225
60

10,000
20.577
80

12,000
19.029
90

14,000
17.577
100

16,000
16.216
110

18,000
14.942
120

20,000
13.750
130

22,000
12.636
140

25,000
11.104
155

30,000
8.885
180

35,000
7.041
205

40,000
5.538
230

45,000
4.355
255

50,000
3.425
280

https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-43#Appendix-E-to-Part-43

These tolerances are quite a bit narrower than those for the popular answer.  As of this comment, I'm the only upvoter for this answer.  Any idea why no one else appreciates this answer?

I suspect because the other answer is what a pilot is going to check during pre-flight (no special equipment needed) so that may seem acceptable to the larger number of pilots here. My answer is in regards to the actual altimeter system from someone who has helped design various altimeters, and I suspect there are fewer of us here.

Thanks for the info.  I'm glad the people designing the altimeters have such detailed certifications.


text:
How tall is the 747-300 without the tail height?
I know that the 747-300 tail height is 63'5", but how tall is the fuselage alone? Also, what is the height of the cargo area and main cabin?

What research have you done to try to find this?

The minimum and maximum height is depicted as dimension "A" (with hump) or "H" (without hump) on the infographic below from Boeing's "Airplane Characteristics for Airport Planning":

(747-100B, -200B, -200C and 300 dimensions)

Interestingly, there's no height for the hump. A is the nose open, L is the standard height. (edit: it's on the next page)

The picture appears to be a 747-8, not a -300, based off the engines and the shape of the hump.

This may not have been exactly what I'm looking for, but the resource provided some useful stuff. Refer to this document and you'll find many useful diagrams with the measurements I'm seeking. Thanks.

Are there cargo versions of the -8, @At0mic, that have an opening nose?

@FreeMan Yes, there are, and they sell a lot better than the passenger variant. Here is a picture of one with the nose open. Anyway, I updated the image in the answer to the one for the -300 variant.

Thanks, @Bianfable. I was unaware of that.

Boeing's ACAPS documents are handy, but they always provide ranges. Moreover, the 747 doesn't sit flat on the ground; it has a slightly nose-down attitude, so that aft doors are higher than forward ones. If you wanted something more of an absolute reference, I can tell you this:
The 747 fuselage is 309 inches high from keel (WL 91) to crown on the humped part of the fuselage. The constant-cross-section part of the fuselage is a 256" wide, 268" tall cylinder.

The cargo deck is 27 inches above the keel (WL 118).
The main deck floor is 109 inches above the keel. The top of the main deck floor is the reference height for the entire fuselage, and is WL 200 (waterline, 200" above the imaginary zero)
The upper deck floor is 217 inches above the keel (WL 308).

By keel, I mean the bottom of the fuselage proper, excluding the wing-body fairing underneath. That would add somewhere between 5 and 11 inches below the keel, approximately. It's a lot harder to find precise measurements on that part of the plane; Boeing doesn't consider fairings and protuberances when describing dimensions.
Source: Boeing 747 Structural Repair Manual (SRM).

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
What is the artificial horizon in between the pilots for?
There's always a third artificial horizon, generally closer to the left (Captain's) side, but I've never understood what it's for. Is it just a backup, or does it serve some extra purpose?

"Always"? Can you include a cockpit picture illustrating your question?

The standby attitude indicator was adopted by regulation in the late 60s or early 70s following an incident involving a Lockheed Electra that suffered a dual attitude gyro failure in bad weather.
The Captain was flying the airplane on "partial panel", using airspeed and altitude for pitch control, and the turn-and-bank gyro for bank control, something instrument pilots learn in their initial training.
The mental workload on partial panel is quite high, made worse with a fairly demanding turboprop like the Electra, and the Capt developed spatial disorientation and the plane augered into a mountainside.  Some time after the investigation, the standby attitude indicator was mandated for transport aircraft.
The standby attitude indicator will have its own stand alone power source, usually connected to an emergency or battery bus, and will be a self contained unit with an internal gyro (whereas the main attitude indicators normally have remote gyros).
There are two basic uses of the standby attitude indicator:

Last resort attitude indication if both main attitude systems fail
at the same time (quite rare).
The more common scenario is where the standby attitude indicator
provides for a 2:1 majority vote where one of the main attitude
indicators deviates but maybe doesn't fail completely (no red flag
on the display or instrument, although you may see a PITCH/ROLL DISAGREE message of some kind on an airplane with EFIS).

If you're flying along and suddenly
your own attitude indicator starts to tilt, or drift up or down
spontaneously, your immediate response is to observe both the
standby and the opposite main attitude indication and compare them to yours.
If the standby agrees with the opposite indicator, you disregard your indicator and transfer control to the opposite pilot (or the autopilot to the opposite Flight Director).
If the standby agrees with your indicator, you proceed on the assumption that the airplane is doing what the indicators say it is doing (at least initially - you still check that airspeed and altitude indications are responding as they should to the apparent attitude change).

Many planes feature what's called a Multi-Function Display or MFD.  There may be a variable number of these, but usually it's at least one each for the pilot and copilot, sometimes with additional MFDs in the middle, or two each for both pilots.  These displays can be used for any number of purposes, including the artificial horizon.  These are of course electronic displays and as such have the possibility that the screen will fail during flight, so there will usually also be an analog artificial horizon so that they still work even if there's an electrical failure.
(Caveat: I am not a pilot, but I have programmed simulators for planes, including programming the simulated MFDs, so I know a bit about these specifically.)

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Why do paratroopers not get sucked out of their aircraft when the bay door opens?
A few instances of injury/death were reported when passengers/pilots got partially sucked out of the airplane due to cabin depressurisation in a commercial aircraft.
Paratroopers, on the other hand, do this all the time. When the bay doors open, they don't get sucked out. Rather, they jump off on their own.
What is the difference in the two scenarios?

When I did my first jump (civilian) from a Cessna I almost got sucked out.

If the cabin pressure is higher than the environment pressure, they are blown out, not sucked.

@Uwe: you appear to be saying that being sucked out of anything is a physical impossibility.

The difference is in the pressurization. An aircraft with skydivers or paratroopers would either not pressurize in the first place or smoothly depressurize the cabin using the outflow valve before opening the bay door. Therefore, there is no pressure difference when the door is opened.
When people are sucked out of a window, this is due to a rapid depressurization event. The aircraft was pressurized with respect to the outside air and when the window fails a lot of air is rushing out in a short amount of time to equalize the pressure.

Immensely grateful for the clarification. Are paratroopers equipped with special suits to prevent organs from expanding beyond their safe limits, to battle the low pressure at high altitudes? My question arises from the fact that even though depressurising is gradual, the resultant pressures are still lower than comfortable for human bodies.

From what i have seen, even very high jumps don't exceed 9000 meters altitude. The pressure on that level is still comfortable for a human body (you will only need an oxygen supply). People climb Mount Everest without any pressure suits, which has an altitude of 8848 meters.

People have even climbed Mt Everest without oxygen. That's many hours spent at that altitude. Jumping from that altitude is likely survivable without oxygen, as it just takes a few minutes to descend to a thicker atmosphere.

@MSalters They also take several weeks to acclimate to that. If you were at a comfortable altitude (say, 3000 meters) and suddenly got shot out to Mt. Everest-level pressurization, I bet it would be pretty rough on you — at a time when you probably want to be in tip-top mental shape (which is not the case of Everest climbers without oxygen). According to wikipedia, they carry oxygen for the jump.

See also: https://journals.physiology.org/doi/full/10.1152/japplphysiol.00169.2017

This is the correct answer despite whatever details may surface about rapid shifts in pressurization. I expect paratroopers who jump at high altitudes train for it. Frankly, Hollywood makes the whole situation seem a lot worse than it actually is. Pop a window and half the plane is sucked out... And there's always at least one who's pulled into an engine. But never the heroine or hero who just stands there shooting the villain who probably broke the window on a wild shot anyway... Funny that.

Two remarks, first, you don't need a pressure difference to be sucked out, the "carburettor effect" can achieve that. Secondly, paratroopers usually jump from quite low altitudes.

Re mt Everest - yes, but the CLIMB UP. Standing and letting yourself drop is quite a lot easier than climbimg up to the top.

As far as I'm aware nobody has ever been "sucked out of a window" by a depressurisation event in an aeroplane... The force isn't that great

@ScottishTapWater British Airways Flight 5390: "an improperly installed windscreen panel separated from its frame causing the captain to be sucked out of the aircraft"

@dunni the issue is not whether the altitude is deadly per se, it's whether you are conscious and reacting. I am given to understand that's sometimes important when jumping out of airplanes.

the use of oxygen before and during the jump also prevents immobilization (the bends) that can otherwise occur during rapid changes in pressure encountered during the jump. and having a full breathing mask also helps with the cold

@ScottishTapWater Aloha Airlines Flight 243 lost flight attendant Clarabelle "C.B." Lansing; United Airlines Flight 811 ejected eight and apparently sent at least one passenger through the engine.

@eps  You cannot possibly get the bends during the jump.  The bends happen when you go from high pressure to low pressure - during a jump the pressure increases.  I also don't think you can get the bends during a a plane ride up to the jump (but am less sure): there is no time limit, or decompression required, for divers who only dive to 10m - that is a change in pressure of 1 atmosphere, which is more than the change in pressure during the ride up to a parachute jump.

@MartinBonnersupportsMonica: spacewalking astronauts are at risk of decompression sickness and therefore breathe a zero-nitrogen atmosphere for a few hours before EVA, and IIRC that's a pressure change from 10psi to 4psi

This is why an early pressurized aircraft, the B29, was depressurized upon any enemy sighting (not sure how modern aircraft deal with the possibility of battle damage).

@prosfilaes Bear in mind in the case of 811 the explosive decompression was combined with the collapse of the aircraft floor above the now missing cargo door, which had structurally compromised the aircraft when it detached. Decompression by itself, say by a window blowing out, would not be enough to rip rows of seats out of the aircraft.

The interior of highflying airplanes is pressurized from the inside because there's not enough air at that altitude. For parachuting, you wouldn't want to fly at those altitudes anyway, unless you're doing a HALO jump, in which case the plane would be de-pressurized safely before the drop and the crew just wear oxygen masks. For lower altitude flights, you just open the door and jump out, because there's no pressure differential:

Paratroops are dropped from the lowest possible safe altitude, because the point is to get down ASAP, not recreational skydiving.

The key point:
You can't open the door on an aircraft when it's pressurized.
If you have even a mild 3 PSI (20kPa) pressuration and a modestly sized aircraft side door of 2000 square inches (2 sq.m.?), that is 6000 pounds (3 tonne) of pressure on that door. As such, most aircraft doors are designed to open inward (at least for the first few mm, e.g. via an over-center arrangement).  That way, the outward pressure helps pin the door mechanism in the shut position, using the pressure to prevent accidental opening.  It can also help seat the seals, and place the door's weight on more sturdy elements, reducing mechanism wear.
You cannot possibly open an inward-moving door at pressure. Even if the door is outward-moving and you manage to overpower the over-center mechanism, the door would open extremely violently due to the many tonnes of force on the door. This would damage mechanism, door, frame and even possibly down the aircraft.
So with no pressure difference, there is no "rush of air blasting out of the now-opened door".
This settles the crux of your question:
How do parachuters jump out of a pressurized aircraft? They don't.
When aircraft are set up for parachuting, they depressurize the aircraft.  This is a prerequisite to opening any door.  Now, jetliner doors aren't really made to be opened in flight, but it actually works on the 727's rear door, as famously used by D.B. Cooper.  And of course, military cargo airplanes with rear doors are designed to do the same, to allow cargo drops and paratroopers. And likewise civilian jump aircraft.

It is precisely because of DB Cooper that modern passenger jets no longer have doors in the tail assembly.


text:
Visa Requirements for GA
I'm planning to take a flight in a small airplane around the world, which means I will have to stop to refuel in various countries. The countries I am particularly asking about are Turkey and Iran. If I just want to land and refuel, then takeoff again, without exiting the airport, will I still need a transit visa/customs clearance?

What country do you live in?

If planing this sort of trip, you do not ask strangers on the internet. You'd normally be working through service provider/s to support the flight https://aviation.stackexchange.com/a/58917/60886 . Even if you can land somewhere to refuel without a Visa, having a plan for when something prevents you taking off would be pretty much mandatory anyway.

You could also check over at the travel.stackexchange.com, which has a very popular 'visas' tag for questions.

@tedder42 Due to various rules, it may be relevant not just what country you live in but what country you are a citizen of.

Your best bet is to use a reputable FBO in those countries and work closely with them to identify all the requirements you will have to meet. Turkey is not a big deal, but for Iran you may also want to check with the US State Dept.


text:
B-52 inflight refuelling
I saw a photo of a B-52 - early model - just dropping off the inflight refueling boom, and the landing gear was extended.
Was this a common operation or something out of the ordinary - flight test, etc.?

There are a lot of videos on youtube of B-52 A-A refueling, none of them with the landing gear down. If what you saw was an early model/version....likely they were just testing.

Would this be the photo, or similar: https://3973lostoros.com/kc-97-refueling-b-52/

The early refueling airplanes were prop driven and slow, maybe they had the gear out to create some drag to keep them slow. @Whisky2, welcome to the site. Please edit and add a picture to your question.

Linking to the photo in question, or at least pointing us to where it's located would be very helpful

@Whisky2 doesn’t post a picture of a Boeing B-52 with the gear down refueling, so it’s really speculation to what he was talking about with his question. @Jpe61 posts a photo of a B-52 being refueled by a Boeing KC-97 with wheels down, which could be the photo @Whisky2 referred to in his question.
What I do know is that the KC-97 has a cruise speed of 410 mph and a maximum speed of 444 mph. The B-52 has a cruise speed of 509 mph. I could not locate any documentation of what steps the Air Force took to safely lower the speed of the B-52 while refueling. This really limited window of speed is what lead to the development of the Boeing KC-135.

Do you have any source for the claim that the B-52 was based-off the 367? I suspect the timeframes do not align

They don't. I'm pretty sure that's a mistype.

The drag of the landing gear did not help with flying more slowly, but helped to keep speed constant at low throttle settings.

I removed the references to the 367 being developed from B-52.

I removed my comment on that topic, but I question that the B52 needed to drop gear and flaps to fly at 410.  And that doing so would not overspeed both.  Do you have a source for that claim?

@MichaelHall You could be right. I know that the problems refueling the B-52 with the KC-97 became a big issue because of the very narrow window available between stall speed and max speed for refueling.

This answer only makes sense if we accept that the B-52 needed gear & flaps out at over 300 mph... which on its face seems extremely dubious. Maybe there is something more subtle going on here (IAS/TAS issues, or needing drag to keep the engines at an adequately high/responsive power setting - Peter's comment), but as it stands this answer needs citations in order to overcome the credibility issues raised.


text:
What type of ailerons does the C172P have?
Today during the mock ground session with my instructor he asked what type of ailerons does the C172P have. I looked in section 7 of the POH and all I was able to find was "Conventional hinged ailerons" under the Airframe section. He said that it was not the correct answer and told me to go through the POH again to find out.
Are there any other official sources that I can find this info?
I'm leaning more towards the frise ailerons as I vaguely remember noticing that the leading edge of the up going aileron protrudes down pass the bottom of the wing.

If your instructor said you should find it in the POH then you should look in the POH.  That said, I fail to see how this knowledge would help make you a better pilot.

I have looked in the POH of various C172 models, and none of them mention anything other than  "Conventional hinged ailerons".

The C172 is designed with “Piano Hinges” at the upper leading edge of the aileron, so even though the lower edge extends down a little bit, it is not a true Frise aileron.
They are also rigged so that the ailerons deflect more “Up” than the “Down”. Correct rigging gives 20° Up and 14° Down deflection at the control limit.
I would call them “Differential”, “Frise type” ailerons.
None of this is mentioned anywhere in the POH.
“Writing by Valerie” photo

You make a good point.  They are actually a hybrid.

Yes they're frise ailerons if the bottom leading edge is ahead of the aileron hinge so that the bottom leading edge protrudes below the airfoil mold line when the aileron is up.


text:
To what degree do airline ops specs preclude hand flying?
I retired in 1999. I'm curious to what degree typical airline ops specs now discourage or prohibit doing what I used to do as a matter of course insofar as hand flying.
For example, I usually hand flew the aircraft until leveling at the first cruise altitude (FL290 or FL310 on fully loaded 747-100/200 aircraft). For the step climbs as fuel was burnt, I nearly always disengaged the autopilot and did the climb manually. At the top of descent I clicked the autopilot off, and I flew approaches manually.
Many of my fellow crew members thought it odd that I did so much hand flying, but as I would explain when asked, I didn't get to the 747 until I was 50 and didn't get to its left seat until a couple of years later, and I wasn't about to forego any of the fun.
None of the hand flying I did was prohibited by our ops specs of the time. My question is: to what degree, if any, do current ops specs discourage or prohibit the hand flying I did?

It's good to see that hand flying skills are still in use.  A great display of stick and rudder skills.

There are no Ops Specs that preclude hand flying, however company policy and operational considerations do in specific situations:

Level flight within RVSM airspace
Cat III approaches (and I believe Cat II approaches)
High workload, critical phases of flight (company specific policies here)

The FAA even came out with a SAFO not too long ago recommending that pilots do more hand flying during periods of low workload (and during training) with the goal of maintaining hand flying proficiency.

i thought using the autopilot in level flight within RVSM was required by regs

@rbp It is, and falls under "operational considerations". ;-)

My company only mandated autopilot use during monitored approaches (all cat II approaches and cat I below RVR 2400 for high minimums captains) and for compliance with RVSM ops.
I typically hand flew at least up to 10,000 feet but often up into the flight levels.  On descent into fields with a lot of vectoring I usually disconnected the autopilot on our final vector to intercept the approach.  Going into less busy places I often disconnected the autopilot when descending out of 10,000 feet.
I also tried to get in one raw-data (no autopilot, no flight director) ILS approach every trip I flew to keep those skills up.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Do pilots who have color deficient eyesight see light gun signals differently?
Can pilots with color deficient eyesight expect to see the red, green, and white light-gun signals as such? In other words, if the controller is giving them a green light, will they see green? If they are being given a white light, will they see white?

It depends on the type and severity of the color deficiency and on the individual.
When I first applied for a 2nd class medical, I couldn't pass the color test. I took a practical test with an FAA inspector to get a waiver. We walked outside the FSDO office, and he had me identify the color of the lights being directed at me by the tower. Fortunately, I had been warned to have the tower do this for me on a previous day so I wouldn't be surprised. In my case I had to remember that if I saw yellow, that was white. If I saw white, that was green. Red was red.
When I first applied for a 1st class medical, I again had to take a practical test, but this time from an airplane. I noticed that from the airplane, the white of the green signal was more white, and the yellow of the white signal was more yellow.
Whether the difference from the ground test was due to the increased distance or to my individual daily variation I don't know. I have noticed during physicals through the years that my performance on the color test varies greatly.
In my opinion every pilot should have the tower shoot light-gun signals at him during training so that she/he can see how they look.

+1 for actually using light gun signals at some point in your training (also a good idea to do it both day and night), even if you have "normal" color vision.

Well done asked and self-answered here.

For those that haven't seen them, sometime when it isn't too busy just ask the tower controller to show you what the light looks like when you are on final.  They are usually more than happy to oblige!

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Where in the CARs does it say that we need to perform a walk-around each day?
I understand to keep an aircraft airworthy, one of the items that must be followed is a walk-around each day. I've been browsing through the CARs for a couple hours now and I couldn't find anything on walk-arounds or pre-flight inspections in either the CARs or the AIM. Any help?

Not too long ago there were no regulations at all, yet there were good pilots and bad ones. A good pilot puts his trust in his own judgement and training, not regulations.

14 CFR §91.7 Civil aircraft airworthiness.
(a) No person may operate a civil aircraft unless it is in an
airworthy condition.
(b) The pilot in command of a civil aircraft is responsible for
determining whether that aircraft is in condition for safe flight. The
pilot in command shall discontinue the flight when unairworthy
mechanical, electrical, or structural conditions occur.

How are you going to determine if an aircraft is in a condition for safe flight without doing a pre-flight inspection?

What about commercial pilots that fly something like the B737? They don't do walk-arounds before each flight as it's only legally required to do it once per day plus it takes way too long. I'm asking where in the air laws specifically say only one walk-around per-day is required.

There's no regulation that specifically states a walk-around is required, commercial organizations mandate it as part of their procedures as they recognize it's a critical step in complying with the regulation. Smart private pilots will do the same.

@YingTaurus I know several airlines where they do a walk around before every flight. As a minimum it involves a visual check of engines, leading and trailing edges, wheels/tyres, wheel wells, static and pitot ports. On a 737 size aircraft it is usually completed in under 10 minutes. Really not an excuse to skip it.

Every day, no, before every flight, yes.

@GdD I was taught all throughout my PPL training that a walk around each day must be completed, and the first person that does the walk around must sign in the journey log saying walk arounds are complete in order to keep the aircraft airworthy.

That's the procedural rules of the group or flight school you are in @YingTaurus, it's not a regulation.


text:
Can anyone open an exit door or do they require activation by the crew?
Is it possible for anyone on an aircraft to open the exit door? Or does pilot or crew have to activate door open mechanism, so that it can be opened?

This question should be reopened as is not a duplicate. The linked question asks about opening in flight, while this question only asks WHO can open a door. The linked answers do not answer WHO can open an airliner door.

An important point is that any passenger can open the door for an emergency evacuation if the crew is incapacitated.

The pilots have no direct control over the operation of the exit doors. Anyone can open an exit door provided the aircraft is not pressurized. There are simple instructions on the door, so that in an emergency, a passenger can open it if a crew member is not near by.
Most airliner doors also incorporate emergency escape slides that can be automatically deployed when the door is opened.  There is an “Arm” switch or lever on the door itself to activate this system. The slides are typically armed by the Flight Attendants once the aircraft pushes back from the gate.


text:
Most Efficient Commercial Aircraft Design?
What was the most efficient aircraft design (based on factors such as lift, drag, and fuel consumption) but not developed or scrapped due to issues with long term viability and maintenance, operations and repair?

but not developed - We can't truly know that, because companies generally don't publish their designs until they are being developed. I'm sure someone will come up with some things that reached the prototype stage, but this is inherently an unknowable thing.

And not developed means we do not have data. From design to a certified aircraft there are many changes. Simulations cannot give you accurate figures. And you forget one important part of equation: engines (which are usually designed or modified for a specific aircraft, so to calculate drag and efficiency is impossible)

The most efficient designs, based on lift, drag and fuel consumption, for heavier than air craft, were the ones that could fly slowly enough and still have sufficient Reynolds numbers to generate lift efficiently.
Some, like the Handley Page HP 42 could lift 15 pounds per horsepower and fly at 100 mph.  The contemporary Douglas DC-3 could lift 10 pounds per horsepower but fly it twice as fast.
The C-130J Hercules can lift 8 pounds per horsepower but fly it at 400 mph.
Aircraft gain advantage in True Air Speed by flying higher, thereby faster, to maintain the same Indicated airspeed in thinner air.
However, at altitude, a (turbine) compressor is needed to provide enough air to maintain enough thrust for the same IAS.
So the most efficient design may be ... a jet powered aircraft with an excellent, glider-like lift to drag ratio, flown at altitude.
Modern airliners are designed in precisely this way$^1$.
$^1$ ton-miles per gallon fuel consumed is one way of looking at it.  The faster plane can then become more efficient.


text:
Does aircraft manufacturers provide option to exchange older models?
Most of the vehicle manufacturers provide exchange value for older models when buying a newer one. Like you can exchange your old BMW 3 Series for new 3 Series or upgrade to 5 Series and so on.
Is there any similar offering provided by aircraft manufacturers to update, something like upgrade 747's to 777's?

The difference is that individual auto trade-ins are motivated by buyer perceptions of status, style, &c.  Airlines are more likely to be motivated by practical factors such as operating & maintenance costs, so would be less likely to trade, and the trade-ins would be worth less, as a percentage of new cost.

Further, automobile trade-in is offered by the dealer in order to incentivize sales to people who have a running car.  You won't get this if you're buying directly from the manufacturer.

@ZeissIkon Carmakers actively participate in the used car trade: they sponsor leases to generate a stock of used cars, they have repurchase agreements with rental fleets, they have certified pre-owned programs which apply a factory warranty.
What's also not comparable is that aircraft are sold under the razor blade model: a lot of the profits come from spares and support. An older airframe can produce more profits than a new one. The 737MAX groundings caused GE to increase profits, as it kept older engines in service and they didn't have to take the hit on new ones.

Manufacturers will do whatever it takes to score an order, so it's not uncommon for an OEM to take old aircraft on trade with a new order, especially if they are from the same maker.  The OEM I worked for had a used aircraft sales division that was mainly used to unload trade-ins.

Many of your budget airlines are flying previously-leased (ie, used) aircraft around. 737's, 747's, airbus variants, etc. Leasing seems to be what many/most airlines do these days anyway, which gives them more flexibility to "trade up" to newer models as they become available.

@SnakeDoc Even non-budget airlines frequently do that to some extent. Delta used to be particularly notorious for snapping up lightly or moderately-used aircraft that fit in well with their existing fleet when they were available at bargain prices. Their entire 717 fleet (which is the world's largest by a wide margin) came that way, for example, when Southwest bought AirTran, but wanted to maintain their 737-only strategy. Even the future Air Force One aircraft were acquired from Boeing at bargain prices as white tails (not technically used, but abandoned orders.)


text:
Is there a minimum weight requirement for an commercial aircraft?
For an aircraft to be approved for commercial usage (like Boeing 747s or Airbus 320s), is there any minimum weight requirements, just the aircraft (without passengers and crew).

The term commercial is a bit broad. Do you consider Cessna 172 for hire as a commercial?

Why would there be such a requirement?

While there is a minimum weight to be defined as Transport Category, 12500 lbs for jets and 19 seats/19000 lbs for propeller driven airplanes, that's a "minimum maximum weight" you could say, to meet a category definition, which determines the certification standards you have to meet.
There is no minimum weight for certification in any category.  You define the mission you are designing for, payload, range, speed etc., and design it to be as light as you can possibly make it and still meet certification requirements for structural strength and performance (while allowing fudge factors for mistakes and flaws), while meeting your design goals.
So if you could design a 747 with new miracle materials, so its empty weight is 300,000 lbs instead of 400,000 lbs, and it meets all the Transport Category requirements for strength and performance, and it can still do what you want it to do in terms of speed/payload/range, you're good to go.

If you are referring to a minimum weight requirement that the aircraft must be operated with after it has been certified (that must be submitted as part of the certification process), yes there is. For example, for my A330's Weight Variant, in the Airplane Flight Manual's Limitations chapter, while there is a Maximum Take Off Weight (MTOW) of 233,000 kg, there is also a specified Minimum Weight of 121,000 kg.

But is that minimum weight just a number grounded in the reality that you can't get any lighter, (in other words, empty weight...) or is it possible to load it lighter but that restriction exists for another reason?

To be honest, I'm not sure. I'll need to check the Basic Weight of the aircraft to see if it's actually possible to fall below it. I can say though that I have never actually been anywhere close to it.


text:
Minimum number of runways required for international airports?
What is the minimum number of runways required for an International Airport to be operational - commercial aviation?
Would two runways suffice?

How do you define "runway"? For example, the same strip of pavement is typically used in both directions (and thus has two runway designations, e.g. "01" and "19") and is also typically used for both landings and departures in both directions. But if you have, for example, a single strip of pavement that can only be used in one direction, or that can only be used for landing, does that count as a half runway? What about airports for floatplanes, if the planes simply land and depart on a lake into whatever direction the wind happens to be coming from, does that count as zero runways, infinite

… runways, or as one runway that is constantly moving around?

"International" doesn't mean "big airport", it means "airport with customs facilities".  Eckhart International consists of a thousand-meter grass strip and a windsock, but is just a five-minute walk from the nearest US Customs station.

Can it be an international heliport with 0 ?

@Gokul Nath KP What research have you done, please?
London Heathrow is often cited as the world's busiest airport and it has two runways.

Just because an airport is an international airport does not mean that it's a big airport. Most big airports are international airports, but plenty of international airports are not big airports. There is no official requirement for a number of runways- it's simply based on demand.

Instead of just looking at the minimum number of runways, I though it would be interesting to have a look at the overall statistics for the number of runways. So I went through my navigation database (AIRAC 2111) and filtered for international airports based on Wikipedia's list. The following histogram shows the number of runways for the 1356 international airports in my database (click image for higher resolution):

As you can see, most international airports (921) actually only have a single runway. The following plot shows the same histogram with a logarithmic y-axis:

There is one international airport with 7 (KDFW) and one with 8 (KORD) runways. The following plot shows a pie chart of the number of runways:

About 2/3 international airports only have a single runway. Less than 1% have more than 4.

The wiki list of international airports is very lacking for the US.  It appears to only include major airports.  Small ones like Ogdensburg International Airport are not there, even Niagara Falls International Airport which has 3 runways isn't on there.

@rtaft I agree, it's not a great list. Wikipedia even has a warning about original research on the page. It's difficult to find a good list with global coverage, which is also computer readable (the Wikipedia list contains IATA codes). For the US, there is 14 CFR § 122.13, but not computer readable...

lol the log-axi, it has no meaning for such data though

Worth to mention that international airport doesn't mean huge airport or long runways. Might not be true in the US but in Europe where all the countries aren't that far away from each other. A graph showing the runway's length could have been relevant. I believe the number of runways depend on the traffic.

There are also a huge number of small "international" airports in the Caribbean. There are lots of relatively tiny islands and archipelagos that form their own customs territories and need immigration and customs clearance facilities.

Americans must love runways.

This data does not take into account ports that have no runway because I presume Wikipedia don't label them "airports". Seaplane ports and helipads have zero runways and there are sea ports and helipads that are international. Would love to see the statistics for zero runways.

@Alexis A log-axis doesn't need meaning. It's purpose is to show both large and small values at the same time. On the linear scale you cannot even see the bar for 7 and 8 runways.

@Alexis, USA might have fewer neighbours, but it also has a much bigger general aviation community, so it also has many small international airports where general aviation flights to/from Canada, Mexico or Caribbean can stop for customs.

@JanHudec Clearly!

In case of an airport exclusively served by helicopters, airships etc. zero runways will probably do. A negative number of runways might be legal, but is difficult to explain. So I guess it is safe to say that zero is the minimum number required.

@yankee "not only do we not have a runway, our helicopters also reglarily drop bombs on that other airport nearby, meaning that we make sure that there is a net negative one runway in this country" like that?

@yankee I think "negative runways" are more commonly known as "mountains"... or is that an "anti-runway".

@yankee Also, define "runway". If it needs tarmac, there must be loads of small "international" airports, e.g. on islands etc., which have only grass. Even if you accept grass but demand signs, lights or such there should be some where it's just a coffee booth with a lawn in front.

Short answer

Minimum number of runways required for international airports?

There is no such requirement for an international airport, so the strict answer is zero landing area, and the practical one is one landing area, which can be a landing strip or an helipad.

Would two runways suffice?

In fact most international airports have only one landing strip because this is not possible or not justified to build and maintain more. This landing strip can be used in both directions (creating two runways), and both for landing and takeoff. A strip may be constrained in one direction, for landing and/or takeoff due to obstacles preventing adequate clearance or environmental reasons.
On the other hand, what actually defines an international airport is the ability to legally support cross-border flights. International airport are first different in the sense they must have customs controls.
From the aeronautical information for Tahiti International Airport (NTAA) we see it's a single strip airport. Note customs availability in the services section:

International strictly refers to customs services availability

For aviation matters, including in the US, an international airport is an airport which can be used for international flights, as opposed to domestic flights only. International flights are flights crossing the State borders.

Accordingly an international airport is one which can deal with customs and quarantine matters for arriving and departing persons and shipments.

So to answer your question briefly, an international airport:

Is an airport, i.e. it deals with air travel, having a IATA code, a destination code in commercial booking systems, is not required nor sufficient to define an airport,
Provides customs and quarantine services to allow persons and goods to lawfully enter or leave the country.
Is not defined by the number of its runways, helipads or waterways, and therefore can have only one of them is that makes sense for the airport manager.

Formal definitions for international airport are detailed below if you are interested.
ICAO definition
ICAO is the UN body facilitating civil aviation across borders. State regulators usually subscribe to ICAO work. ICAO definition of an international airport:

Any airport designated by an ICAO Contracting State in whose territory it is situated as an airport of entry and departure for international air traffic, where the formalities such as customs, immigration, public health, agricultural quarantine and similar procedures are carried out.

Source ICAO glossary
FAA definition
FAA subscribes to ICAO definition, adding details:

Relating to international flight, it means:

An airport of entry which has been designated by the Secretary of Treasury or Commissioner of Customs as an international airport for customs service.
A landing rights airport at which specific permission to land must be obtained from customs authorities in advance of contemplated use.
Airports designated under the Convention on International Civil Aviation as an airport for use by international commercial air transport and/or international general aviation.
(See ICAO term INTERNATIONAL AIRPORT.)

Source: FAA Pilot/Controller glossary
International airports typology
Many international airports are located on touristic islands and most of them have only one landing strip (which can be used in one or both direction, creating one or two runways).
Princess Juliana International Airport (TNCM) is a good example of such medium sized airport with customs and only one landing strip:

KLM Boeing 747 taking off from TNCM, source
Another element for promoting an airport to international status has been mentioned by @rtaft in a comment:

There are many small international airports along the US Canadian border that only deal with small aircraft flights between the two countries, as well as some along the Mexican border for Mexican flights.

The decision to build a second strip is usually driven either by the existence of strong cross winds or the volume of operations.

+1 only answer that mentions Customs!  There are many small international airports along the US Canadian boarder that only deal with small aircraft flights between the 2 countries as well as some along the Mexican boarder for Mexican flights.

@rtaft: I'm adding this information into the answer if you don't mind. Good point.

thanks.  I heard they were quite busy during covid.  Snowbirds were allowed to fly over using these small international airports when the border was closed, then pay a service to transport their vehicles, RVs, etc, across to the airport to get around the closed border restrictions.

Other important factors for the runway numbers are space and money. TNCM is a great example: Where would you put a second rundway on that island (given you have enough traffic). On the other hand, if you have no space but money, you just build a new airport, maybe even filling up some ocean.

In Germany, Lufthansa (the German flagship airline) and Deutsche Bahn (German railways) have a cooperation, where some Deutsche Bahn trains also have a Lufthansa flight number and Lufthansa sells airline tickets for those trains. As a result, some German train stations have an IATA airport code. And at last at some of them, I believe you can have your luggage checked through all the way onto the train and go through customs at the arrival train station.
So, that would technically be an International Airport with zero runways and no aircraft movements.

Technically IATA codes are travel destinations, not airports. It happens most IATA codes can be matched to ICAO airport designators, or to other destinations like Disneyland, but such destinations are not airports, don't have airport designators, and are not subject to air regulations.

This does not make tha train stations airports in any way, not even some paper theoretical one. If some booking website shows them among airports, it is just a limitation of that website, nothing more.

@mins DLP does not appear to be an official IATA location code. Beware the wide variety of unsourced lists online claiming to be IATA codes but actually containing unofficial placeholders used in various systems.

Serious answer: one, Bianfable is correct.
Slightly less serious answer: zero. In principle, there are scheduled flights from CHX (Vancouver Harbour) or YWH (Victoria Harbour) to LKE (Seattle Lake Union), all three of which of which solely operate seaplanes and have no "runways" in the normal sense of the word.
(I say "in principle": it appears that at the time of writing the scheduled routes have been suspended. But that will presumably lift, eventually.)
There are a few other Canadian airports with only seaplane facilities that are classed as ports of entry by the Canadian authorities, and thus could in principle have international travel, eg Whitehorse or Seal Cove, but Victoria & Vancouver Harbours seem to be the only two pure-seaplane sites with a (normally) scheduled service.
In the Caribbean, there are scheduled services from the US to NSB (North Bimini, Bahamas), which is a purely seaplane site. (The US end seems to be Fort Lauderdale, which is definitely not.)

Whether there is a scheduled service does not matter, whether there is customs does. But if the scheduled service is international (which it is for the last case), there has to be customs as well.

@JanHudec in the Canadian case these are explicitly designated as "ports of entry" by the border authorities, which I would interpret as covering customs. The US and Bahamas ones are less clear, but I would agree that if there's a scheduled international service there must be something.

Is there US customs preclearance at the British Columbia seaplane facilities?  If so, the US facility may lack customs facilities of its own.

San Diego International Airport (SAN), in San Diego, CA is one of the world's busiest single runway airports. Interestingly, Montgomery-Gibbs Executive Airport, also located in San Diego, is not an international airport, and has 3 runways. It is one of the world's busiest GA airports.
So, 1 runway would be the minimum for an international airport.

Never knew that about Montgomery field - it's the 1 airfield in SD ive flown out of.

Don’t know if it’s the worlds busiest GA airport. I would guess Van Nuys or Daytona would give them a run for their money.

@CarloFelicione Montgomery-Gibbs Executive Airport: 253199 movements. VanNuys: 232000. Daytona: not a GA only airport, but handles 335000 movements.

1 runway is the minimum for any airport, even it its a grass paddock :)   Then again, if the area is large enough, that might class as infinite runways cos you could land in any direction?

It's quite disputable that it's the world's busiest. Xiamen Gaoqi International Airport and London Stansted both had more passengers than SAN and they're definitely single-runway. London Gatwick has even more, but one could argue it's technically not single runway.

@Criggie: You can operate helicopter or other VTOL flights without any runway at all... ;-)

Ketchikan International Airport in the State of Alaska, USA has one runway.
http://www.airnav.com/airport/PAKT

Consider London airports:

Heathrow (LHR): 2 runways
Gatwick (LGW): 1 runway (there's technically a second runway, but it's so close to the first one they can't both be used at the same time)
City (LCY): 1 runway (and a very short one with a steep approach!)
Luton (LTN): 1 runway
Stansted (STN): 1 runway
Southend (SEN): 1 runway

They are all international airports. Gatwick is consistently in the top 15 airports ranked by international passenger traffic.

If if they are close, they are still 2 runways. Many airports that have multiple runways have them crossing each other and they cannot be ised simultaneosly. They are still airports with multiple runways.

@Polygorial Vladimir is talking about Gatwick which is a pretty weird airport which has 2 runways but is nearly universally considered as having only one due to their layout.

authors: Vladimir F Героям слава


text:
Is Mid-air Emergency Evacuation Procedure Possible?
When both the engine fails or fuel is empty, the airplane is designed such a way to glide in mid-air for sometime.
During this glide phase, is it possible to perform emergency evacuation with the help of other military aircraft? Is it done or tried already?
For discussion purpose, let’s keep aside time taken for military aircraft to reach the airplane location and the time airplane is in glide phase.

If you had enough altitude/control to even attempt this type of thing, the better/easier/more successful outcome would be to point the aircraft at one of the many airports and land normally.

See the IMAX movie "Flyers" from several decades ago.  The plot involves a mid-air rescue of someone who has fallen out of a plane.

Not generally possible, but there are cases:  https://www.popularmechanics.com/flight/a9650/what-went-wrong-in-the-skydiving-planes-collision-16128956/

No. That is not even remotely feasible, by any stretch of the imagination.

The extreme wind blast would make it extremely difficult to hold on, even for healthy people. Children, the elderly, and people who are sick or disabled wouldn't stand a chance.
Maneuvering another airplane close enough to reach by hand is impossible, and there's no way to attach a cable to climb across.

Well, yes and no.  Airliners can slow down to approximately landing speed at low altitude, and that's slow enough to exit more or less safely (by parachute, for instance).  Doors can't be opened when pressurized, but if all engines are stopped, the cabin will lose pressure fairly rapidly.  The impossible part is the Air Force One cable escape.

There used to be a ground-to-air delivery system utilizing specially equipped C130s and tethered balloons. There are also winch systems used to recover paratroopers hung up on the outside of aircraft during a jump. Both of these are military performed with trained and experienced personnel. Both are considered for emergency use only. This would not be feasible with one let alone one hundred civilians.

@ZeissIkon I get what you're saying about my first point, so I'll remove it. But the question specifically asked about evacuations with the help of another plane. I interpret that as specifically transferring from one plane to another. But for my second point, the stall speed for a commercial jet is well above the limit for designating a storm as a hurricane; that much wind would cause problems for even healthy individuals, not to mention children, elderly, and disabled people.

Any attempt to evacuate an aircraft in flight will have to be by parachute, because it's impossible to safely join two aircraft in a way that will let people transfer from one to the other (it has been done, a small number of times between slow-flying barnstorming aircraft, but it was a stunt, not even a demonstration of something intended as a practical procedure).
This won't work because airliners don't carry parachutes.  If they did, the weight penalty to do so would make it much more difficult to operate at a profit, and cut deeply into the cargo and luggage capacity (or limit passenger seating, since if it were practical, it would be required).
Even with static-line parachutes, the risk to passengers attempting to evacuate and in-flight aircraft is likely higher than keeping passengers in their seats and belts while making a dead stick landing -- but generally, a competent pilot will have landed the plane before the fuel is fully depleted, so there will be power available to adjust glide or even go around if needed.  The rare exceptions to this -- like the Gimli Glider -- have demonstrated that dead stick landing is preferred over a mass parachute jump by untrained people over randomly selected terrain.

Totally agree. Plus a parachute jump with highly trained personnel in the best conditions and controlled terrain is not without risk. You can plan on injuries and pray for no casualties. Jumps into urban terrain has proven even worse. Combine that with panicked passengers with no training, it would be a disaster.

For which aircraft are you speaking? Each aircraft is going to have a different glide ratio and best glide speed. Altitude is going to determine best glide range and endurance. Either way, any assistance aircraft would have to be on station at the time engine loss occurred.
Now, for arguments sake, let’s consider an average military transport aircraft. A well trained and equipped group of paratroopers can completely evacuate an aircraft in less than two minutes with no more than two minutes advanced warning. That is if they were suited up before the emergency ensued. If they were not suited up, an in-air donning of all the gear for an entire plane load may take ten minutes if all of the parachutes were palletized. Five minutes if each person were already carrying the gear in hand. That would include buddy checks and maybe jumpmaster checks if enough jumpmasters were present. Having done mid-air parachute donning, I know that it is possible. Having not done it in an emergency, I have been conservative on my estimate of the time involved. I also have not included any time spent by the pilots scoping out an appropriate or safe LZ for the paratroopers. Nor time spent racetracking a pattern around the LZ to line up for the right distance and direction for favorable wind drift.
This would be the bench mark for a rapid emergency deployment. It would be the best scenario if flying at low altitudes. If flying at higher altitudes, like those normally flown by airliners, it may be wiser to try to glide down to a nearby airport with all personnel still onboard. It depends on the circumstances. Considering a safe LZ for an entire plane load of paratroopers would be a clearing at least a mile long and an eighth of a mile wide, a safe landing on the same field may be possible for a military aircraft with STOL capabilities.
Now, saying all that, my only real mid-flight emergency came as a passenger paratrooper in a C141 over the Pacific. The pilots opted for a glide to Oahu for a dead-stick landing. We had three other C141s in echelon. Since only a few of us were awake at the time, most of the other paratroopers were not even informed of the emergency until it came time to prepare for landing.
Using that as an example, can you imagine the possibility of doing the same with one to four hundred civilians with no prior training. The weight and space (mainly space) required for the parachutes would eliminate the possibility of carry-on luggage other than personal items. Then, the jump itself would be a complete cluster. The possibility of a complete evacuation of a fully loaded commercial airliner in the time remaining for the glide would be slim. Especially since the jump would need to be performed below twenty thousand feet MSL. Even if you were using parachutes with AADs. Especially if you were using static lines. Above that, your time of useful consciousness without supplemental oxygen goes down to as low as five minutes and continues to decrease to mere seconds at the altitude that most airliners fly.
Again, this is the best case scenario for a commercial airliner. Given the above conjecture, it would make some type of Hollywood style plane-to-plane transfer of passengers darn near impossible in the glide range of most transport aircraft.

To add some numbers to this: an airliner flies about 6 miles up, but if it lost power and depressurised it would have to descend to about 2 miles (10,000ft) pretty quickly. Then it glides at about a ratio of about 10:1, so it could cover about 20 miles in about 10 minutes. It takes longer than that for passengers to leave a plane normally.

If we gave the airline the benefit of the doubt and said the glide ratio was 17:1 (what I found for the B737), and the jump altitude was 20,000 feet MSL with a ground elevation of 0 MSL, I still don’t think it would be enough time to organize and evacuate a plane full of panicked civilians. Even if they were able to, the casualty rate would be very high.

It is a stunt that has been done by trained wing walkers.
This has been done by wing walkers. In 1921, Wesley May performed a plane-to-plane transfer with a fuel tank on his back and made the first ever air-to-air refuelling. Ok "military aircraft" probably need to be from the times of WWI.
How much this can be done without extensive preparation (suitable type of the both aircraft involved, trained walker, both trained pilots) I would not speculate. Probably not very possible.


text:
What happens when an airplane is retired?
With launch of new models every few years, what happens to the older airplanes which was in service for more than decades? Where does it get stored.
Who buys old airplanes? Does manufacturers buys it back for reusing the parts or is there any specific companies which buys old airplanes?

If you are french speaker, I recommend this video which explains what parts are recycled and rapidly expose what is done when no recycling is done.

Very much related

There are a few things that can happen:

They are sold to another airline - In some cases the plane may still have life (cycles) left and may find it's later days flying for another outfit. Sometimes airlines for countries with emerging economies can only afford older aircraft and they may end up far from their original homes.
They are sold to cargo airlines - cargo airlines may buy old passenger planes as they may not always be looking to fly the fanciest new airliners since the customer rarely talks back ;)
They end up in the bone yard - aircraft with life left on some parts hold at least some value and may be relegated to a bone yard to be picked over for years to come.
Ultimately, scrap metal always has value...


text:
Most bizarre/easiest to fly X-Plane aircraft?
I’m currently trying to get my little brother into flight sims. When we were little, we got to crash planes on our grandfather’s computer, which has kind of gotten us both into flying (…kind of ironically?). I’ve gotten pretty good at the basics, but I want to get him into it, because his current hobby is endlessly listening to Harry Potter audiobooks, which gets annoying after the third play through. He will get bored after a while if he doesn’t laugh hard enough, so I wanted to ask the community about aircraft.
My questions are: what are the easiest aircraft to fly in X-Plane? and What are the most bizarre/funniest aircraft to fly in X-Plane?
As sort of a side question, what are some other ways to make him interested in flying using better strategies? (Keep in mind, he’s only just turning eleven next month.)
…maybe i should try crashing planes again. nostalgia.
Mods, feel free to delete this question if it’s too off-topic! :-)

I’m voting to close this question because it is about PC flight simulation without a relation to real world aviation. See also The scope of Flight Simulation questions on the Aviation SE on Meta.

For default aircraft in XPlane 11, I would start with the tried and true Cessna 172SP.  I would avoid using the Stinson L5 as a starting Aircraft as it is very difficult to control on the ground (a sim model fault not found in the characteristics of the real thing) and he will probably have a devil of a time landing it without causing a ground loop.
Your comment about crashing the airplane reminds me of my childhood playing the original monochromatic Microsoft flight simulator. A neighborhood friend of mine and I would take turns taking off from Chicago Lakefront Airport (the now defunct Meigs field) and crashing the airplane into the Sears Tower and thought it was the funniest thing to do.  This was 1983, mind you, when life was much simpler and we had no idea that our harmless simulated havoc was going to become a tragic reality some 18 years later on Sept 11, 2001.


text:
Why is the pitching moment of this symmetric aerofoil non-zero?
As I understand it, the pitching moment coefficient of a symmetric aerofoil should be zero, under potential flow assumptions. Obviously, approaching stall and post-stall, these assumptions are invalid and the pitching moment coefficient would no longer be zero.
However, looking at this graph of pitching moment coefficient against angle of attack, for a NACA0009 aerofoil at Re = 1e+6, it seems like Cm does actually vary considerably at low and moderate angle of attack.
Why?

<> and it is, correctly, in the figure you show, for zero alpha. why do you think it would be constantly zero?

The centre of pressure does not vary with (moderate) alpha for a symmetric aerofoil, so never changes difference from the reference point, so if zero pitching moment at zero alpha should be zero pitching moment at any (moderate) alpha - F*d is always zero if d is always zero.

The definition of the aerodynamic centre is the point around which pitching moment does not vary with angle of attack - therefore, if it is zero at zero alpha, and does not vary with alpha, it should still be zero for a moderate range of alpha.

From NASA: "For symmetric airfoils, the aerodynamic moment about the ac is zero for all angles of attack." - https://www.grc.nasa.gov/WWW/K-12/airplane/ac.html

Also, for a textbook reference - page 354 of Introduction to Aerodynamics, John Anderson.

Under incompressible potential flow and at small angles of attack, one of the most celebrated results of Thin Airfoil Theory is that all airfoils have their aerodynamic centre at 1/4 chord; and for symmetrical airfoils, the centre of pressure coincides exactly with aerodynamic centre.
If you look at the plot in the OP, the variation of Cm between -3 and 3 deg are relatively small, indicating that the linearized theory agrees well with the nonlinearized simulation.
Beyond 3 deg, however, the viscous effects present in the simulation but absent from Thin Airfoil Theory begin to alter the results. This manifests primarily in the boundary layer, which alters the apparent shape of the airfoil, thereby making it non-symmetrical. The next graph shows the XFOIL simulation at 7deg AOA; notice that the boundary layer at upper surface thickens near the trailing edge.


text:
Can I use any reference area for lift and drag coefficient?
I know that for rockets they often use the circular cross-section S_reference for the drag prediction: drag = rho/2 v^2 * c_D * S_reference
For aircrafts they use the chord length of a wing as S_reference.
So when I want to compare those to for their aerodynamic performance, can I just use
S_reference{rocket} * C_D{rocket}
and S_reference{aircraft} * c_D{aircraft}
So to my mind: I can always use any reference area I want for determining c_D , but when I want to compare two bodys for their aerodynamic performance, I have to use: c_D * S_reference
Thanks for your opinion,

The reference area is chosen according to the flow profile:

For long slender bodies, the wetted area is chosen because the main drag source is the shear forces between the boundary layer and the free flow.
For relatively short bodies, the cross-sectional area is most relevant because of the much larger contribution of pressure differential between front and aft of the stream.

Directly comparing $C_D$ of rockets and aeroplanes would not be very useful, because the reference area for aeroplanes is the wing area, which rockets do not have. Indeed $C_D$ * A is a much more useful comparison, if one knows what reference area A was chosen.


text:
Turbofan engine start - Why does ignition occur so early?
In another thread, two key steps of starting a turbofan (ignition and fuel introduction) are given as follows:

With increased N2 rotation, ignition will be turned on. [...]
With further increase in N2 rotation, fuel flow will be introduced.

For some engines I saw that ignition is typically turned on at about 15% rotation, and fuel is introduced at about 30%.
I understand that the value for fuel introduction (therefore light off) is given by the need to further power the engine as early as possible, but not too early or the system will be disrupted. However I don't understand why there is a precise moment for ignition. My questions are:

Between 15% and 30% rotation, ignition will be on without any fuel. Why doesn't ignition instead occur just before fuel introduction?
Conversely, why wouldn't ignition occur earlier? Is there a physical requirement of the compressor turning at a certain speed before ignition can be on?

Thank you for your answers.

Welcome to Av.SE!

It can be tough to generalize because engines are different, but in the turbines I have flown the igniters are energized immediately by the push to crank button.  Fuel is typically introduced right around 15% RPM.  Too early and you risk a hot start due to low airflow, but delaying will generally not hurt anything, you are just using up time in your start cycle.
I’m not sure where you got your 15-30% figure, but 30% RPM off ground power or battery alone seems very high.
To your question “why doesn’t ignition occur just before fuel introduction?” it does.  “Just before” is a relative and subjective term, it doesn’t take very long to spin up to 15%.
To your question “is there a physical requirement for the compressor to be turning at a certain speed before ignition can be on?”  No.  Per my comments above, they will usually start firing as soon as the start sequence is engaged.  There isn’t a separate button for igniters, just the start button.
Again, this is based only on my personal experience with several different turbine engines.

Thank you. I got the numbers from this video, mentioning ignition at 2:50 ("the engine core needs to spin at 14% of its maximum speed") and showing it at 5:30, and for fuel introduction it is at 3:17 and 5:36. It is on an ERJ, seems to be with FADEC.

Traditionally the fuel is introduced by the pilot at a specified minimum RPM, but this is a function controlled by the pilot-eye-hand brain interface (only on the newer pushbutton start FADEC engines is this function fully automated) and we all know how imperfect this interface is.
With a traditional system, you need to allow some fudge factor in case the pilot adds fuel early, and also if there are system faults it gives a bit of time for the fault to be detected and displayed. So most start systems start the igniters running as soon as the starter is on (in the pre-FADEC days it wasn't too hard to ruin an engine, which is why captains traditionally handle starting).
The RPM at which fuel is to be turned on is actually bit sooner than really necessary, to let the engine help the starter bring it up to self-sustaining RPM.  The minimum RPM is there because you need a minimum mass flow going to the burner can to control the flame and therefore the temperatures (these engines are "air cooled" after all and the majority of the mass flow is not actually being burned, but being used to contain the flame boundaries - some flame does make it back toward the turbine during start, as you see when the ITT spikes, but it has to be minimized, and the more mass flow the better).
You can delay introducing fuel well past the minimum RPM, and you will actually see a lower ITT peak on a non-FADEC engine by doing so (because, as I said above, more mass flow provides more flame control), but this really adds to wear and tear on the starter.
When I was in the Regional Airline business supporting CRJs we observed that a lot of captains made it a practice to delay fuel introduction quite late (like waiting to 25-30% instead of 20% for the GE CF-34) because they noticed that the ITT peak was lower when fuel was delayed.  However this had to be balanced against shorter starter life and we advised against getting carried away with this because the marginally lower starting ITT peak didn't appear to actually improve engine life, while shortening starter life significantly.
On the other hand, it's important to know that it isn't essential to get the fuel on right now when the RPM is at the fuel introduction value and you can do it at a relaxed pace. If the nominal value is 20%, putting fuel on at 23 or 25% does no harm, so take it easy (pilots in training (including me) would fumble with the thrust lever lockout thinking they had to get the fuel on exactly at the right time).

Thank you. My question was actually about ignition, but your explanations for fuel introduction are very informative as well.

It depends on the jet engine model that is being started.  On some Honeywell models, the pilot will bring the thrust levers to idle thrust when there is at least 10% N2 rotation and positive rotation on the N1.  At this point, the ignition comes on and fuel is introduced to start the engine.


text:
What happens when the velocity of the lower surface of the airfoil is lower than the velocity of the free stream?
At a certain AOA I noticed that the speed of air in the lower surface of the airfoil is lower than the free stream's speed. What is the consequence of that?

Local pressure will rise above the freestream pressure. Speed and pressure are linked, as expressed in Bernouilli's principle. Also the local temperature will rise, as expressed in the ideal gas law.
Note that at all angles of attack there is one point where the local flow speed will decrease to zero in 2D flow: This is the stagnation point. On wings in three dimensional flow this becomes a stagnation line, and swept stagnation lines still have some residual flow speed, but in all cases the local speed is below the free flow speed at and around the stagnation line.
Since lift is proportional to the pressure difference between the upper and lower side of the wing, this slowing down is welcome. Another beneficial effect is the lower wall friction of the slower flow. However, the thicker an airfoil is, the higher will be the flow speed on both sides, due to the displacement effect of the thicker airfoil. Thinner airfoils are structurally less efficient, so a compromise needs to be found which allows enough internal structure while keeping thickness reasonably low.

Does this mean that more lift is generated, I mean since the pressure difference widens?

In a wind tunnel - stationary wing, moving air - the air on the bottom of the airfoil is slowed down. But in reality - still air, moving wing - you can't "slow" air that is not moving. This would seem to mean that the air on the underside of the wing can have the same or lower pressure than the free stream. Is this correct or is my reasoning flawed?

@TomMcW: It's all relative. The moving wing becomes a stationary wing for an observer sitting inside the airplane.

I can see that the pressure differential between the top and bottom is the same from either point of view. That’s why we can use wind tunnels to gather data. So it really doesn’t matter; my question is really just academic. But is there any point on a wing in subsonic flight through still air where the pressure is higher than ambient barometric pressure? The diagram on this answer seems to show just a small point at the leading edge which I suspect is a compressability effect right at the stagnation point.

@TomMcW: Look at the pressure plot in the question to the answer you linked. The "Fig. 2" airfoil has higher pressure than ambient where the area between the pressure coefficient line and the x-axis is shaded in pink. The flow speed is Mach 0.78, but a very similar distribution can be found with incompressible flow. Basically the higher-than-ambient pressure is around the stagnation point (near the nose) and close to the trailing edge. At higher angle of attack the whole bottom can have positive pressure coefficients, meaning pressure higher than ambient.

@TomMcW, no, no, the pressure values are the same from either point of view as well! Forces are equal in all inertial reference frames and since so are areas, pressures must as well.

@JanHudec Bernoulli principle states an inverse relationship between velocity and pressure. Can you explain how you can get pressure higher than still air?

@TomMcW: The sum of velocity squared and pressure is constant, that is all what Bernoulli says. The constant does not need to be the same for still air and air with an aircraft moving through it. Just consider the ram effect around the stagnation point: The added energy from the moving wing will increase pressure there.


text:
Drag coefficient and lift coefficient
What happens if drag coefficient increases but the lift coefficient remain the same?

Could you expand your question a bit? What prompted it? What is unclear to you? "what happens" to what? the fuel efficiency, the L/D ratio, the flight range, ... ?

In that case, you'll need to increase the power in order to keep your airspeed and stay airborne. The extra power will be spent in fighting the extra drag... Besides, you'll have to reduce AoA in order to keep total lift equal to the weight and thus stay at the same altitude...


text:
Does having a halo effect after LASIK disqualify you from being a pilot for the Air Force or commercial pilot?
I had LASIK a while ago and I have some halo effects when I look at lights at night, and was wondering if that alone is something that would disqualify me from being a pilot for the Air Force or an airline?

Which country are you asking about?

FAA doesn't allow airmen with complications like halos. etc. From FAA Guide for Aviation Medical Examiners:

The FAA expects that airmen will not resume airman duties until their treating health care professional determines that their post-operative vision has stabilized, there are no significant adverse effects or complications (such as halos, rings, haze, impaired night vision and glare)...

A medical examiner should certify that the applicant (for pilot) is not suffering from any such complications:

An applicant treated with a refractive procedure may be issued  a medical
  certificate by the Examiner if the applicant meets the visual acuity standards and the Report of Eye Evaluation (FAA Form 8500-7) indicates that healing is complete; visual acuity remains stable; and the applicant does not suffer sequela such as; glare intolerance, halos, rings, impaired night vision, or any other complications.

USAF doesn't allow individuals with cases where the surgical outcome affects one's performance of duties; having a halo effect would be a disqualifier.


text:
Who does air traffic control to the oceanic flights?
ARTCC does air traffic control to the flights in their FIR. Then who does air traffic control to flights that are above the ocean(like pacific ocean or atlantic ocean)?
Is there any FIR above the ocean too?
I want to know that what facility does air traffic control to the flights above the ocean.
Please let me know in detail. Thank you.

Related: Who manages International Airspace Traffic? and Where to download NATs (North Atlantic Tracks) information? and the illustration of when international cooperation doesn't work: Why is there a strip of uncontrolled airspace between Russia and Norway?


text:
What is the history of the name of airway?
I am studying about airway. And I want to know about the history of designation of name of airway.
I have known that the first name of airway is colored airway(L/M frequency airway) like A586 or G13.
But why we call them colors? I don't know the association of colors and airways. And how was the name of airway changed later?(like victor airway)
Please let me know in detail.

Related

Related, colored lights as beacons. I don't know if this is accurate. V is for VHF (VOR).


text:
Is it practical to integrate turbofan or ramjet engines into an airliner wing?
The de Havilland Comet had turbojet engines integrated into its wings, such that its nacelles were mostly flush with the wings like so:
(wikimedia.org)
I recognize that turbofan engines are significantly larger in diameter than most turbojets, making the Comet's arrangement impractical for most modern airliners, but would it still be possible to integrate the engine nacelle with, say, the bottom of a wing while maintaining good aerodynamic characteristics on the wing? Would ramjet engines, owing to their lower profile, be more practical to integrate into a wing than turbofans?

The first turbofan, the Rolls-Royce Conway, had a bypass ratio of only 0.25 in order have a small enough diameter for placement in wing roots. It was initially planned for the V bombers and planned civilian derivatives of them. So yes, it is practical to place a turbofan engine in the wing, but comes at a cost:

Buried engine placement will shift the optimum to smaller bypass ratios, which reduces fuel efficiency.

Next, now your leading edge is occupied by an intake and cannot use any of the possible leading edge devices to increase lift at low speed for take-off or landing. The same goes for the trailing edge. The consequence is:

Buried engine placement will require a larger wing because the use of high-lift devices is not possible near the engines.

Larger wings weigh more and produce more drag in cruise. The last reason might be the most important: In operation, a podded engine is much easier to service and to repair than a buried one. The lower maintenance cost was the main driver for podded engines in the later members of the first generation of airliners (Boeing 707, DC-8, Convair 880).

Buried engine placement drives maintenance cost up.

There are fewer designs with ramjet engines, many of which never took to the air. Here, placement in the wing plane was mostly chosen to avoid thrust-related pitch moment changes. However, a ramjet is best used at high speed, and then you need to keep wing thickness down in order to reduce wave drag. Therefore, the engine placement cannot really be called buried anymore, but is closer to the buried than the podded variety.
The best example is the Lockheed D-21 drone pictured below (source). Since the aircraft is practically a ramjet with wings, the engine dominates the appearance.

Due to the high thrust needed for supersonic flight, supersonic aircraft keep their engines close to the wing and designs with podded engines like the Convair B-58 or the Myasishchyev M-50 were the exception. Stealth aircraft want to hide the hot exhaust and often use an overwing exhaust location which makes their engine placement also a buried one. You might argue that the engine of the Lockheed RQ-3 pictured below (source) is actually in the fuselage, but being a flying wing it does not have one:

The RQ-3 and similar designs like the Northrop B-2 clearly show that a turbofan engine location inside the wing is very practical indeed.

The book Synthesis of Subsonic Airplane design by E. Torenbeek contains some sections on jet engine placement. According to the writer, buried engine installation was favoured by British designers and podded engines by American designers.

Figure 2-12 depicts four bomber planforms, one American and three British. The wing area of the British designs are quite large to provide the space for the engine mounting compared to the wing of the B-47, while span is identical. The book then mentions some of the advantages of wing root mounted engines:
2.3.2

a. The extra draq resulting from the buried engine installation is only a few percent as against about 15% of the total drag in the case of a configuration similar to the B-47. Incidentally, the current generation of turbofans show a value of about 8 to 10%.
b. As a result of the low wing loading and low value of $C_L$ in cruising flight, maneuvering is possible without compressibility problems such
  as buffeting.
c. The pitch-up problem of swept wings is less significant for low aspect ratio wings.
d. As a result of the low wing loading, the low- speed performance will be better.
e. The relatively low aspect ratio wing box structure will lead to greater stiffness and aeroelasticity will be less of a problem.
Many of these arguments are only valid up to a point, and in particular the progress in engine technoloqy towards high bypass ratio engines, together with the development of more efficient high- lift devices in 1950-1970, has settled the case in favor of high wing loadings and pod-mounted engines .

So wing root mounted engines have less drag, however wing pod mounted engines provide bending relief of the wing which saves on structural weight. When mounted in pods in front of the leading edge, they provide torsion relief for aeroelastic effects such as flutter. Less drag was the only direct advantage of having no engine pods, all other advantages cited are due to using wings with low aspect ratio/span loading.
From Torenbeek section 6.5.1

Engines buried within the fuselage can only be used when the payload has a relative1y small volume and enough space is available for the engine and its inlet and exhaust ducts and for the wing center section. Generally speaking, this will only be the case with small private aircraft and trainers, as far as civil aviation is concerned. The relatively large diameter of modern high bypass engines virtually pro- hibits the installation of engines buried in the wing roots, as in the Hawker Siddeley Comet and Tupolev 104.

So turbofans are most impractical to install in the wing root, pods underneath are really practical maintenance-wise. Perhaps ramjets, but how does the aircraft get to the speed where ramjets can operate?

"Hawker Siddeley Comet" sounds strange - for me it is (and will always be) a de Havilland design.

what about running the wing spar throgh the wing-rooted engine? wouldn't that be difficult as well?

According to Joe Sutter in his book on designing and implementing the 747, placing the engines in pods under the wing had two advantages:
The engines were much easier to service.
In the event of a major engine failure, less damage is done to the wing.
In recent years, the sheer size of the larger turbofans used in commercial aircraft preclude their being mounted within the wing.
There have been two catastrophic failures of engines on Airbus A380's in recent years, in that a good deal of the engine disintegrated. Both aircraft remained flyable and were landed without further damage, so that part of the design has definitely been proven.


text:
What is this plane spotted from Outer Banks, NC?
What is this plane spotted from Outer Banks, North Carolina?

Looks like a C-130

Why is the rear door open?  Marines jumping out?

(USAF)
Judging by the single pair of pylon tanks, DIRCM (Directed InfraRed Counter Measure) heads near the tail and lack of armament on left side, and what looks like 4 bladed props, it is likely an MC-130H.

@ymb1 - I think the noses look similar enough considering the fairly rough condition of the pic in the OP. i.e. it's pixley enough that we're probably looking at that same squared off nose bump but it just looks rounder due to low resolution and blurry focus.

There are a couple of extra pods on the variant in your answer, I'm not sure this is correct.

@MichaelHall the outboard refueling pods are detachable. https://www.thedrive.com/content-b/message-editor%2F1577753262173-mc-130h.jpg?auto=webp&optimize=high&quality=70&width=1440

I see, thanks!  The USMC KC-130s I crewed on had a more permanent refueling pod.

It matches a Lockheed C-130 Hercules from that point of view.

(source: wikimedia.org)

This is the only indisputably correct answer at this point.  Were you looking for detail on what specific variant it might be?

I can tell you without a doubt it is a MC-130H TALON II. The nose radome, electrically operated IFR pods on outboard wings, uhf rail antenna as opposed to long wire, DIRCM pods on aft fuselage, and the subdued paint with no readily identifiable tail numbers or base identifiers on the aircraft are key points of identification of aircraft. That and the fact I was DFCC in the Air Force on these aircraft and they hold a special place in my heart. If you zoom in on the nose section you'll notice 4 numbers (1803). Those are part of the tail numbers for their aircraft and if you look up either 87-1803 or 88-1803 can't remember which one it should come back as MC-130H. Last time I saw this particular plane was at Kirkland AFB acceptance inspection from Mildenhall AFB as part of a 3 tail plane swap, but that was a long time ago and it very possibly is gone on to one of 3 SOCOM bases Kadena, Hurlburt Field, or Mildenhall, Kirkland is AETC aircrew training base for those 3 locations.

Hi, and welcome to aviation.stackexchange. You seem to be identifying the aircraft in picture in the answer given by swordfish45. The aircraft in the picture of the question is a different aircraft.

Can you see the UHF rail antenna on the airplane in the question, or the answer?


text:
Too soon to pass the IATRA exam? (Canada)
I just finished the IFR group 1 rating this week. Currently at 220h Total flight time with CPL, no job in sight (of course), and wondering if I should start studying for the IATRA now or wait until I'm closer to 250h and/or a job?
Thanks in advance, have a delicious day!

If you have the time on your hands might as well get started with the study part.  IATRA is the ATPLs condensed into a single smaller 50 question exam.  You will expand your knowledge base and it never hurts to acquire knowledge sooner rather than later.
Don't take the exam right away though, as it is only good for 2 years and it might be a lot longer than that before you'll land a job that needs a multi-crew qualification.  There's a lot of pilots on furlough and it's going to be several years for the industry to reabsorb them all.  Most of the opportunities are going to be in the North.

Thanks for your response, I'd like to pay for the course only once when I'll decide to pass the exam. Might still end up buying it early though!


text:
Why do some military flight appear on Flightradar but some not?
I often see military flights in the sky, which do not appear on FlightRadar24. I do understand that low-flying military airplanes do no necessarily get picked up by these trackers, and that some military aircrafts switch of transponders. However some flight do appear on this ADSB-Tracking website. For example currently you can often see USAF F-16 near the Ukraine with a Tanker in the back on some kind of holding pattern.
What logic or factor governs whether a flight appears on FlightRadar24?

Transponder On/Off. Just a little while ago, there were 2x F-16 from 31st FW, Aviano AB, IT displayed. Then just one. What you don't see is the literal dozens of other NATO fighter jets roaming around, supported by those multiple tankers.

Several key things define whether an aircraft shows on Flight Radar and any other tracking site:

These sites do filter some aircraft and choose not to display them.
A plane may choose to turn off their transponder. Military aircraft in particular are exempt from many civil rules and regulations which would see most aircraft having an active transponder and of course their operational requirements will dictate they often do. That said, ultimately, any plane CAN disable it if they wish.
Flight tracking hardware used to feed these sites doesnt work with older transponders. Old transponders require a spinning RADAR dish to pinpoint a bearing and can not be triangulated using static receivers. While most civil aircraft use newer transponders, again, the military is often exempt.

Flight tracking hardware does work with older transponders, but there has to be more of it and there not always is. Older transponder must be triggered by a spinning radar, but then if three static receivers independent of the radar receive it, they can triangulate the position by comparing the time of reception. But there has to be three of them and there not always is (while for ADS-B one is enough, because position is broadcast).

What about low flying aircrafts?

@JanHudec AFAIK, For MLAT to work you need the ability to differentiate targets. MLAT only works with Mode S. In theory, as a one off, you could track a Mode A target if you knew the Transponder Code was unique, but AFAIK all of the tracking solutions rely on Mode S's address space to differentiate

Although now I'm googling further I can find claims of being able to track Mode A/C via MLAT - I'm still sceptical that the tracking sites do so though


text:
Can cruise pilots/second officers go for years without doing a takeoff or landing?
I was looking at the description of this role i.e. someone who provides cruise flight relief flying. As conceivably, someone could be bonded for multiple years because of the type rating being covered by the airline, it is possible they could 'fly' for multiple years and yet never actually do a real takeoff or landing?

I believe that a pilot has to do a certain number of take-offs and landings to keep their license current.

Can you explain and link to some information about what a "cruise pilot" is? I'd never heard that term until I saw this question.

Sure. http://www.ainonline.com/aviation-news/2014-11-10/easa-proposes-changes-relief-pilot-requirements

DJClayworth: I happen to know that is the answer but you deserve the credit.

This question might be better if a jurisdiction were included. In the U.S., for example, there is no such thing as a 'cruise pilot.' Relief pilots on long haul flights have the same requirements as the rest of the crew here (i.e. a minimum of one qualified Captain is always on duty.) In the U.S., there is no such thing as a pilot in flight deck of an airliner at all unless they have an ATPL. Licensure requirements vary dramatically by jurisdiction, though. Additionally, the required takeoffs and landings for currency (as DJClayworth mentioned) will also likely vary by jurisdiction.

Not a definite answer, but a friend of mine flew 747's as a 2nd officer for a major airline for a number of years. He had multiple take offs and landings in a sim, but 0 actual in a front seat.

@reirab This is not strictly true. the FAA states no differences to ICAO Annex 1 - 2.1.4.1 or 2.1.4.1.1.  Therefore a US "cruise pilot" could exist. They would require the relevant class/type rating - and this class/type rating would have the limitation of the role endorsed on the rating. (see my answer for more information).

The short answer is: yes
Personal Licensing regulation outlined in Annex 1, 2.1.4 "Circumstances in which class and type ratings are required" states that:

2.1.4.1 A Contracting State having issued a pilot licence shall not permit the holder of such licence to act either as pilot-in-command or as co-pilot of an aeroplane, an airship, a helicopter or a powered-lift unless the holder has received
authorization as follows:
a) the appropriate class rating specified in 2.1.3.1; or
b) a type rating when required in accordance with the provisions of 2.1.3.2.
2.1.4.1.1 When a type rating is issued limiting the privileges to act as co-
pilot, or limiting the privileges to act as pilot  only during
the cruise phase of the flight, such limitation shall be endorsed on
the rating.
ICAO - Annex 1 - Personnnel Licensing

Though vague about takeoff, landings, or other stages of flight, this published regulation is clear that

Cruise pilots acting only during cruise phases of flight is allowed, providing they have the appropriate class or type rating
The limitation of their role, such as cruise flight only,  is endorsed on the respective rating.

Your question didn't ask about what state/country you were asking about

The FAA lists no differences from the above regulation in GEN 1.7
Though it may differ between EASA states, it seems that EASA states also comply with the ICAO regulation in this matter. For example, see the Irish Aviation Authority (IAA) differences to Annex 1: GEN 1.7

Every airline pilot is required to maintain currency. In a 2nd officers case most of this will probably be in a full motion simulator.

Welcome to Aviation.SE. To me this does not seem to directly address the question, could you add a little more extensive reasoning?


text:
Can 80hp Rotax 912s be upgraded to 100hp?
The more recent Rotax 912's are 100 hp engines. Can the earlier 80 hp models be upgraded to 100hp - without a complete engine swap?

I don't know, but I would say upgrading would be the same as new engine. The engine will have been designed for max design power plus some margin, let's say 25%.  So max designed = 80hp, design limit = 100hp.  See the problem? You fiddle with all the bits to produce 100HP and your design margin has gone away. Even if the margin was 50%, you halve it by uprating to 100hp. To allow for this, you'd need to change the cylinder block, and the crank, and the rods, and and and...before you know it, you've got a new engine.

It looks like there are several kit upgrade options from third parties, e.g.:

120HP turbo kit
125HP kit
95HP kit

I have no idea about the pros and cons or costs. The 125HP kit "requires machining of the crank case and heads", the others seem to be additional components.